A prior art device of the general type referred to herein is shown in FIG. 4. Connection box 11 is provided with projection 12 extending from bottom wall 11a thereof. Connecting sections 13a of main line 13 are inserted into the hollow portion of projection 12. Support hook 14 holds connecting sections 13a within the hollow and prevents them from falling out. However, this configuration suffers from certain defects. During assembly, connecting sections 13a are inserted into the interior of projection 12. However, since the connecting sections are hidden inside the projection, it cannot be determined if connecting sections 13a have been pushed too far in and are impacting against the inner wall of the projection. Alternatively, if connecting sections 13a have not been inserted far enough, this also cannot be determined readily by observation. The result of the latter will be unstable contacts.